Pulmonary hypertension plays a major role in the morbidity and mortality of a number of acute and chronic lung diseases including bronchopulmonary dysplasia. While clinical studies have implicated transforming growth factor-alpha (TGF-alpha) in the pathogenesis of these diseases, the role of TGF-alpha, its cellular targets, and the signaling pathways involved are unclear. Preliminary data accompanying this application demonstrate that epithelial expression of TGF-alpha causes severe reductions in pulmonary artery number, vascular remodeling, and pulmonary hypertension as early as 2 weeks of age in transgenic mice. We also have preliminary evidence to suggest that this is mediated in part by autocrine signaling through EGF receptors on distal epithelial cells, and reductions in vascular endothelial growth factor-A (VEGF-A). Using both in vitro and in vivo approaches, this proposal will test the central hypothesis that epithelial expression of TGF-alpha disrupts vascular growth and causes vascular remodeling and pulmonary hypertension through EGF receptor-dependent autocrine-paracrine signaling. In the first phase we will define when pulmonary growth is disrupted by TGF-alpha, whether acute or chronic expression of TGF-alpha is necessary, and whether TGF-alpha causes vascular remodeling and pulmonary hypertension independent of reductions in vascular growth (Specific Aim 1). In the second phase we will define the role of indirect signaling through the epithelium versus direct signaling to the vascular endothelium (Specific Aim 2) using a dominant negative (mutant) EGF receptor to block TGF-alpha signaling in specific cellular compartments. In the third phase we will define whether TGF-alpha, regulates expression of VEGF-A in type II epithelial cells in vitro and in vivo, and whether reductions in VEGF-A contribute to the pathogenesis of pulmonary vascular disease (Specific Aim 3). The overall goal of this proposal is to define the timing, cellular targets, and mechanism by which TGF-alpha disrupts pulmonary vascular growth and causes pulmonary hypertension and vascular remodeling. This information will serve as a basis for developing therapeutic strategies aimed at improving lung growth and preventing pulmonary hypertension in premature babies and adults.